During engine starting events, a fuel rail operative to channel pressurized fuel to the engine may not have enough pressure to deliver fuel in quantity and quality required to accurately meet engine fuel demands due to an increased response time of the fuel pump and system. This is particularly acute in all direct injection engines which rely on cam driven fuel pumps to establish the high pressures required for direct in-cylinder fuel injection. Such high pressure fuel pumps struggle to achieve adequate pressure at the typically low engine cranking speeds. Inherent advantages of direct injection gasoline engines, such as direct engine start and combustion-assisted engine start, are lost due to low fuel pressure issues at engine starting events. In addition, low fuel pressure in conventional engine start maneuvers may result in several misfire events prior to robust combustion and therefore result in poor engine startability, undesirably increased tailpipe emissions and undesirably decreased fuel economy. Similarly, during fuel/power enrichment maneuvers—especially in E85 spark-ignited direct-injection (SIDI) engines which require higher fuel flow rates due to the relatively lower power density of E85 relative to other fuels—fuel pressure can drastically drop due to transient high fueling rate requirements, resulting in lower power output and higher engine out emission due to inadequate fuel delivery.
Solutions to low fuel pressure include the addition of a second fuel pump. Additional pumps and the machinery required to drive them may be bulky and require a large number of additional parts, exacerbating package space issues, adding unnecessary weight to the vehicle, and adding additional parts that may eventually require service. Additionally, fuel pumps driven by electric motors frequently require a large gear reduction factor in order for both the motor and the fuel pump to operate in normal operating ranges, and such gear reduction devices are typically bulky and require a particular orientation to the attached devices.